The present invention relates to a disposable, preselected-volume, capillary pipette device for picking up and transferring a selected volume of a liquid sample such as blood. The present invention also provides a novel method of making and recalibrating the pipette device and using the device to take blood samples.
Capillary pipette devices are well known for collecting blood samples from a patient who has been pricked with a needle to instigate blood flow (xe2x80x9cfinger stickxe2x80x9d). Such disposable pipette devices are disclosed, for example, by Kenney in U.S. Pat. No. 5,059,398 and by Coleman et al. in U.S. Pat. No. 5,460,782, both of which are incorporated herein by reference. Coleman et al., U.S. Pat. No. 5,460,782 (hereinafter Coleman) discloses an automatic filling micropipette formed from a tubular body having an open end, and being closed or having a piston at the opposite end. The open end of the tubular body is sized to permit liquid to flow into the tubular body by capillary action. A vent hole 6 is positioned at a preselected point along the body of the tube to limit the amount of liquid which enters the tube by capillary action.
The device disclosed by Coleman is useful for collecting a sample of blood from a xe2x80x9cfinger stick.xe2x80x9d However, the embodiments illustrated in FIGS. 1-3, 5 and 6 of Coleman have multiple components which are costly to make and assemble to form the finished product. For example, in FIGS. 1-3, a flexible closed tube 4 and a sample collection tube 2 must be separately manufactured and assembled. In FIGS. 5 and 6, a plunger or piston 30 and a sample collection tube 22 must be separately manufactured and assembled. The cost of making and assembling these multi-component designs is prohibitively expensive. Therefore, it would be desirable to provide a single-component, preselected-volume pipetting device which is inexpensive to manufacture.
In FIG. 4, Coleman discloses a single-piece, preselected-volume micropipette formed from a single flexible tube 12. While this embodiment appears to be easier and less costly to manufacture than the embodiments disclosed in FIGS. 1-3 and 5-6, this embodiment does not function as well as the other embodiments disclosed by Coleman.
For example, referring to FIG. 4 of Coleman, liquid from the filled collection tube 12 is expelled by squeezing the proximal end 15 of the tube. Since the proximal end of the tube 15 is not bulbous, the volume of air contained therein may not be sufficient to emitt the fluid sample with a single squeeze. Splatering of the liquid sample may occur if the proximal end must be squeezed repetatively to emitt the sample.
Further, the reduced diameter of the proximal end of Coleman""s tube 12 increases the tube""s rigidity, thereby providing resistance to squeezing by a technician. Therefore, it would be desirable to provide a disposable, preselected-volume capillary pipette device formed from a single, contiguous tube of hydrophilic and elastomeric material having an elongate capillary section formed at one end of the tube and an enlarged diameter, bulbous section formed at the other end of the tube.
Forming a pipette device from a single, contiguous tube of elastomeric material using prior art techniques is difficult. For example, using blow molding to form the enlarged-diameter bulbous end of the tube is very difficult since elastomeric and hydrophilic materials, such as PEBAX and BAREX, change from a semi-rigid state to a fluid state within a very small temperature range (for example, 4xc2x0 F. for PEBAX). Precise temperature and pressure control are required to insure the integrity of the product. Additionally, precision forming by blow molding is very difficult since the thickness of elastomeric tube stock has a large tolerance. Therefore, it would be desirable to provide an easy and efficient method of making a pipetting device having a bulbous end without blow molding an elastomeric and hydrophilic material such as PEBAX or BAREX.
Preselected-volume capillary pipetting devices must provided in a wide range of calibrated volumes. For example, a particular laboratory blood test may require any where from 5 to 150 microliters of blood from a xe2x80x9cfinger stick.xe2x80x9d Blow molding equipment requires timely reconfiguration to change the calibrated volume of the device. Therefore, it would also be desirable to provide a simple and inexpensive method of making preselected-volume capillary pipetting device in a wide variety of calibrated volumes.
The present invention provides a disposable, preselected-volume, capillary pipette device formed from a single, contiguous tube of hydrophilic and elastomeric material. The invention also provides an inexpensive and easy method of manufacturing and re-calibrating the pipette device within a wide range of volumes.
The disposable, preselected-volume, capillary pipette device is made of a single, contiguous, tube of hydrophilic and elastomeric material. The material preferably comprises a polyether block polyamide sold by Elf AtoChem under the trademark PEBAX or a wettable thermoplastic acrylonitrile barrier sold by Elf AtoChem under the trademark BAREX. The tube has a flexible wall and a channel extending from a first end to a second end. The tube has a thickness in the range of 5 to 7 mils (0.13 to 0.18 mm.).
The tube has a fluid flow port having a diameter D1 at the first end for admitting and emitting liquids to and from the tube. The fluid flow port has a diameter D1 in the range of 0.03 to 0.1 in. (0.08 to 0.25 cm.). The tube has a seal at the second end. The seal preferably comprises a heat seal.
A capillary section is formed at the first end of the tube. The capillary section extends a distance L1 from the fluid flow port to a preselected intermediate point on the tube. The channel has an inner diameter equal to D1 in the capillary section.
A bulbous section is formed at the second end of the tube. The bulbous section extends a distance L2 from the preselected intermediate point to the seal. The channel has an inner diameter D2 greater than D1 in the bulbous section. Preferably the channel has a diameter D2 in the range of 0.15 to 0.3 in. (0.38 to 0.76 cm.). Preferably, D2 is at least two or three times as large as D1.
A vent hole extends through the flexible wall in the capillary section of the tube. The vent hole has a diameter D3 smaller than D1. Preferably, the vent hole has a diameter in the range of 0.004 to 0.016 in. (0.01 to 0.04 cm.).
The vent hole is positioned in the tube at a preselected distance L3 from the port to define a liquid sample chamber within the capillary section. The liquid sample chamber has a preselected calibrated volume defined by the equation xcfx80(D1/2)2L3. The calibrated volume is preferably from 5 to 150 microliters. The calibrated volume is less than the volume of the bulbous section.
The device includes a pair of opposed fins fixed to and projecting radially-outwardly from the capillary section. The fins extends the entire length of the capillary section. The fins may include identifying indicia printed thereon. The method of making the pipetting device comprises the initial step of providing a contiguous, preselected length of hydrophilic and elastomeric tube having a first and second end, a flexible wall, and a constant inner diameter D2. The first end of the tube is then heat sealed.
The tube is bifurcated into a bulbous section proximate the first end and a capillary section proximate the second end. The inner diameter of the capillary section of the tube is reduced to a constant diameter D1. Preferably, the inner diameter is reduced by heating and crimping the capillary section to reduce the inner diameter of the capillary section to a diameter D1 less than D2. Prior to heat crimping, a cylindrical rod is inserted into the capillary section. The cylindrical rod has an outer diameter equal to the selected diameter D1. The capillary section is reshaped into an elongate, cylindrical tube having an inner diameter D1 and a pair of diametrically-opposed, radially projecting fins extending along the length of the capillary section.
A vent hole is drilled through the capillary section of the tube at a distance L3 from the port. The vent hole has a diameter D3 smaller than D1.
The fins are tapered proximate the second end of the capillary section of the tube. The fins are tapered by shearing in a direction generally along the length of the fins.